This invention relates to coatings for electrically conductive surface subject to exposure to a high frequency field, as for high frequency conductors, and, more particularly, to an electrically conductive coating especially adapted to prevent interference resulting from secondary electron emission and to a method for production of such coatings.
It is known that the emission of secondary electrons in electrical apparatus for high operating frequencies, such as waveguides, resonators and antennas for microwave frequencies, may cause interference even under high-vacuum conditions. If the secondary electron emission factor is greater than 1, an avalanche-like increase in the number of electrons, a so-called multiplicator discharge, may occur, leading sometimes to an undesirable total reflection of the microwave signal to be transmitted.
It is known that such interference due to secondary electron emission may be suppressed by applying a rough metal layer, which absorbs emitted secondary electrons, to the surface of the microwave conductor. With high-frequency signals of high amplitude, however, this technique is defeated by overheating of the applied rough layers because of the skin effect, and when high static magnetic fields are present, by the resulting hindrance to electron absorption. Similar problems occur with electrically conductive surfaces which are subject to exposure to a high frequency field, especially if the surfaces define a chamber which is evacuated or contains a rarified gas, e.g., the so-called first wall of a fusion reactor or the inner surface of the vacuum channel of a particle accelerator.
The object of the present invention is to provide a rough coating to a surface subject to exposure to a high frequency electric field in such a manner that it will afford a satisfactory suppression of interference due to secondary electron emission even at greater high-frequency signal amplitudes and in the presence of high static magnetic fields.